3,032 research outputs found
Evidence for azimuthal variations of the oxygen abundance gradient tracing the spiral structure of the galaxy HCG91c
Context. The distribution of elements in galaxies forms an important
diagnostic tool to characterize the system's formation and evolution. This tool
is however complex to use in practice, as galaxies are subject to a range of
simultaneous physical processes active from pc to kpc scales. This renders
observations of the full optical extent of galaxies down to sub-kpc scales
essential. Aims. Using the WiFeS integral field spectrograph, we previously
detected abrupt and localized variations in the gas-phase oxygen abundance of
the spiral galaxy HCG91c. Here, we follow-up on these observations to map
HCG91c's disk out to ~2Re at a resolution of 600pc, and characterize the
non-radial variations of the gas-phase oxygen abundance in the system. Methods.
We obtained deep MUSE observations of the target under ~0.6 arcsec seeing
conditions. We perform both a spaxel-based and aperture-based analysis of the
data to map the spatial variations of 12+log(O/H) across the disk of the
galaxy. Results. We confirm the presence of rapid variations of the oxygen
abundance across the entire extent of the galaxy previously detected with
WiFeS, for all azimuths and radii. The variations can be separated in two
categories: a) localized and associated with individual HII regions, and b)
extended over kpc scales, and occurring at the boundaries of the spiral
structures in the galaxy. Conclusions. Our MUSE observations suggest that the
enrichment of the interstellar medium in HGC91c has proceeded preferentially
along spiral structures, and less efficiently across them. Our dataset
highlights the importance of distinguishing individual star-forming regions
down to scales of a few 100pc when using integral field spectrographs to
spatially resolve the distribution of oxygen abundances in a given system, and
accurately characterize azimuthal variations and intrinsic scatter.Comment: 12 pages, 11 figures, accepted for publication in A&A. Supplementary
movie assocociated with Fig. 8 is available (until publication) at:
http://www.sc.eso.org/~fvogt/supp_mat/HCG91c/O_gradient.mp
Star formation in the warped outer pseudoring of the spiral galaxy NGC 3642
NGC 3642 was classified as a spiral galaxy with three rings and no bar. We
have performed an HI and optical study of this nearly face-on galaxy. We find
that the nuclear ring might in fact be part of an inner one-armed spiral, that
could be driving nuclear accretion and feeding the central activity in the
inner kpc. The inner ring is faint, and the outer ring is a rather ill-defined
pseudoring. Furthermore, the size ratio of the rings is such that they cannot
be due to a single pattern speed linking them together.
The outer pseudoring is peculiar, since it lies in the faint outer parts of
the disk, where star formation is still going on at 1.4 times the optical
radius. Higher HI column densities are associated with these regions and the
atomic gas layer is warped. These perturbations affect only the outer disk,
since the kinematics within the main body conforms well to an ordinary
differentially rotating disk.
We propose here that both nuclear activity and star formation in the warped
outer parts might be linked to the fact that NGC 3642 is located in a rich
environment, where its close neighbors show clear signs of merging. Our
suggestion is that NGC 3642 has captured recently a low-mass, gas-rich dwarf,
and star formation was triggered in this infalling external gas that produced
also a pronounced warp in the gaseous disk.Comment: Accepted for publication in A&A. Full resolution version available at
http://www.iaa.es/~lourdes/3642/H3551.tar.g
Spatial Mixing and Non-local Markov chains
We consider spin systems with nearest-neighbor interactions on an -vertex
-dimensional cube of the integer lattice graph . We study the
effects that exponential decay with distance of spin correlations, specifically
the strong spatial mixing condition (SSM), has on the rate of convergence to
equilibrium distribution of non-local Markov chains. We prove that SSM implies
mixing of a block dynamics whose steps can be implemented
efficiently. We then develop a methodology, consisting of several new
comparison inequalities concerning various block dynamics, that allow us to
extend this result to other non-local dynamics. As a first application of our
method we prove that, if SSM holds, then the relaxation time (i.e., the inverse
spectral gap) of general block dynamics is , where is the number of
blocks. A second application of our technology concerns the Swendsen-Wang
dynamics for the ferromagnetic Ising and Potts models. We show that SSM implies
an bound for the relaxation time. As a by-product of this implication we
observe that the relaxation time of the Swendsen-Wang dynamics in square boxes
of is throughout the subcritical regime of the -state
Potts model, for all . We also prove that for monotone spin systems
SSM implies that the mixing time of systematic scan dynamics is . Systematic scan dynamics are widely employed in practice but have
proved hard to analyze. Our proofs use a variety of techniques for the analysis
of Markov chains including coupling, functional analysis and linear algebra
Effects of Liposomes Contained in Thermosensitive Hydrogels as Biomaterials Useful in Neural Tissue Engineering
Indexación: Scopus.Advances in the generation of suitable thermosensitive hydrogels for the delivery of cells in neural tissue engineering demonstrate a delicate relationship between physical properties and capabilities to promote cell proliferation and differentiation. To improve the properties of these materials, it is possible to add liposomes for the controlled release of bioactive elements, which in turn can affect the physical and biological properties of the hydrogels. In the present investigation, different hydrogels based on Pluronic F127 have been formulated with the incorporation of chitosan and two types of liposomes of two different sizes. The rheological and thermal properties and their relation with the neurite proliferation and growth of the PC12 cell line were evaluated. Our results show that the incorporation of liposomes modifies the properties of the hydrogels dependent on the concentration of chitosan and the lipid type in the liposomes, which directly affect the capabilities of the hydrogels to promote the viability and differentiation of PC12 cells. © 2017 by the authors.http://www.mdpi.com/1996-1944/10/10/112
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